Bookkeeping for allocation site pretenuring

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index 71b54680f2035d352122fe631018cdd09b8590cc..bf47a3fbe86889e4f67996c392de5490780b6ef0 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -1737,6 +1737,14 @@ void FullCodeGenerator::VisitArrayLiteral(ArrayLiteral* expr) {
   Handle<FixedArrayBase> constant_elements_values(
       FixedArrayBase::cast(constant_elements->get(1)));
 
+  AllocationSiteMode allocation_site_mode = FLAG_track_allocation_sites
+      ? TRACK_ALLOCATION_SITE : DONT_TRACK_ALLOCATION_SITE;
+  if (has_constant_fast_elements && !FLAG_allocation_site_pretenuring) {
+    // If the only customer of allocation sites is transitioning, then
+    // we can turn it off if we don't have anywhere else to transition to.
+    allocation_site_mode = DONT_TRACK_ALLOCATION_SITE;
+  }
+
   Heap* heap = isolate()->heap();
   if (has_constant_fast_elements &&
       constant_elements_values->map() == heap->fixed_cow_array_map()) {
@@ -1749,7 +1757,7 @@ void FullCodeGenerator::VisitArrayLiteral(ArrayLiteral* expr) {
     __ Move(rcx, constant_elements);
     FastCloneShallowArrayStub stub(
         FastCloneShallowArrayStub::COPY_ON_WRITE_ELEMENTS,
-        DONT_TRACK_ALLOCATION_SITE,
+        allocation_site_mode,
         length);
     __ CallStub(&stub);
   } else if (expr->depth() > 1 || Serializer::enabled() ||
@@ -1764,14 +1772,11 @@ void FullCodeGenerator::VisitArrayLiteral(ArrayLiteral* expr) {
            FLAG_smi_only_arrays);
     FastCloneShallowArrayStub::Mode mode =
         FastCloneShallowArrayStub::CLONE_ANY_ELEMENTS;
-    AllocationSiteMode allocation_site_mode = FLAG_track_allocation_sites
-        ? TRACK_ALLOCATION_SITE : DONT_TRACK_ALLOCATION_SITE;
 
     // If the elements are already FAST_*_ELEMENTS, the boilerplate cannot
     // change, so it's possible to specialize the stub in advance.
     if (has_constant_fast_elements) {
       mode = FastCloneShallowArrayStub::CLONE_ELEMENTS;
-      allocation_site_mode = DONT_TRACK_ALLOCATION_SITE;
     }
 
     __ movq(rbx, Operand(rbp, JavaScriptFrameConstants::kFunctionOffset));